This article deals with so-called ''core'' utilities on a GNU/Linux system, such as ''less'', ''ls'', and ''grep''. The scope of this article includes, but is not limited to, those utilities included with the GNU {{Pkg|coreutils}} package. What follows are various tips and tricks and other helpful information related to these utilities.

+

''Core utilities'' are the basic, fundamental tools of a [[GNU]]/[[Linux]] system. On Arch Linux they are found in the [[base group]]. This article provides an incomplete overview of them, links their documentation and describes useful alternatives. The scope of this article includes, but is not limited to, the [https://www.gnu.org/software/coreutils/coreutils.html GNU coreutils]. Most core utilities are traditional [[Wikipedia:Unix|Unix]] tools (see [[Heirloom]]) and many were standardized by [[Wikipedia:POSIX|POSIX]] but have been developed further to provide more features.

−

== Basic commands ==

+

Most command-line interfaces are documented in [[man page]]s, utilities by the [[GNU Project]] are documented primarily in [[Info manual]]s, some [[shell]]s provide a {{ic|help}} command for shell builtin commands. Additionally most utilities print their usage when run with the {{ic|--help}} flag.

−

The following table lists basic shell commands every Linux user should be familiar with. See the below sections and ''Related articles'' for details.

+

== Essentials ==

−

{| class="wikitable"

+

The following table lists some important utilities which Arch Linux users should be familiar with. See also {{man|1|intro}}.

[[Wikipedia:cat_(Unix)|cat]] is a standard Unix utility that concatenates and lists files.

−

* Because ''cat'' is not a built-in shell, on many occasions you may find it more convenient to use a [[Wikipedia:Redirection (computing)|redirection]], for example in scripts, or if you care a lot about performance. In fact {{ic|< ''file''}} does the same as {{ic|cat ''file''}}.

+

{{ic|rm}}, {{ic|mv}}, {{ic|cp}} and shell redirections happily delete or overwrite files without asking. {{ic|rm}}, {{ic|mv}}, and {{ic|cp}} all support the {{ic|-i}} flag to prompt the user before every removal / overwrite. Some users like to enable the {{ic|-i}} flag by default using [[alias]]es. Relying upon these shell options can be dangerous, because you get used to them, resulting in potential data loss when you use another system or user that does not have them. The best way to prevent data loss is to create [[backup]]s.

−

* ''cat'' is able to work with multiple lines:

+

== Nonessentials ==

−

{{bc|

+

This table lists core utilities that often come in handy.

−

$ cat << EOF >> ''path/file''

−

''first line''

−

...

−

''last line''

−

EOF

−

}}

−

Alternatively, using {{ic|printf}}:

+

{| class=wikitable

−

+

! Package !! Utility !! Description !! Documentation !! Alternatives

−

{{bc|

−

$ printf '%s\n' 'first line' ... 'last line'

−

}}

−

−

* If you need to list file lines in reverse order, there is a utility called [[Wikipedia:tac (Unix)|tac]] (''cat'' reversed).

−

−

== dd ==

−

−

[[Wikipedia:dd (Unix)|dd]] is a utility for Unix and Unix-like operating systems whose primary purpose is to convert and copy a file.

−

−

Similarly to ''cp'', by default ''dd'' makes a bit-to-bit copy of the file, but with lower-level I/O flow control features.

−

−

{{Tip|By default, ''dd'' outputs nothing until the task has finished. To monitor the progress of the operation, add the {{ic|1=status=progress}} option to the command. It is not available on older versions (8.24) of {{Pkg|coreutils}}.}}

−

−

For more information see {{man|1|dd}} or the [http://www.gnu.org/software/coreutils/dd full documentation].

−

−

== grep ==

−

−

[[Wikipedia:grep|grep]] (from [[Wikipedia:ed|ed]]'s ''g/re/p'', ''global/regular expression/print'') is a command line text search utility originally written for Unix. The ''grep'' command searches files or standard input for lines matching a given regular expression, and prints these lines to the program's standard output.

* There are ''grep'' alternatives optimized for VCS source code, such as {{Pkg|the_silver_searcher}} and {{Pkg|ack}}.

−

* To include file line numbers in the output, use the {{ic|-n}} option.

−

−

{{Note|Some commands send their output to {{man|3|stderr}}, and grep has no apparent effect. In this case, redirect ''stderr'' to ''stdout'' with {{ic|''command'' 2>&1 {{!}} grep ''args''}} or (for Bash 4) {{ic|''command'' {{!}}& grep ''args''}}. See also [http://www.tldp.org/LDP/abs/html/io-redirection.html I/O Redirection].}}

−

−

For color support, see [[Color output in console#grep]].

−

−

== find ==

−

−

''find'' is part of the {{Pkg|findutils}} package, which belongs to the {{Grp|base}} package group.

−

−

One would probably expect a ''find'' command to take as argument a file name and search the filesystem for files matching that name. For a program that does exactly that see [[#locate]] below.

−

−

Instead, find takes a set of directories and matches each file under them against a set of expressions. This design allows for some very powerful "one-liners" that would not be possible using the "intuitive" design described above. See [http://mywiki.wooledge.org/UsingFind UsingFind] for usage details.

−

−

== iconv ==

−

−

''iconv'' converts the encoding of characters from one codeset to another.

−

−

The following command will convert the file {{ic|''foo''}} from ISO-8859-15 to UTF-8 saving it to {{ic|''foo''.utf}}:

−

−

$ iconv -f ISO-8859-15 -t UTF-8 ''foo'' > ''foo''.utf

−

−

See {{man|1|iconv}} for more details.

−

−

=== Convert a file in place ===

−

−

{{Tip|You can use {{pkg|recode}} instead of iconv if you do not want to touch the mtime.}}

−

Unlike [[#sed|sed]], ''iconv'' does not provide an option to convert a file in place. However, {{ic|sponge}} can be used to handle it, it comes with {{pkg|moreutils}}.

[[Wikipedia:Iproute2|ip]] allows you to show information about network devices, IP addresses, routing tables, and other objects in the Linux [[Wikipedia:Internet Protocol|IP]] software stack. By appending various commands, you can also manipulate or configure most of these objects.

−

−

{{Note|The ''ip'' utility is provided by the {{Pkg|iproute2}} package, which is included in the {{Grp|base}} group.}}

The {{ic|help}} command is available for all objects. For example, typing {{ic|ip addr help}} will show you the command syntax available for the address object. For advanced usage see the [http://www.policyrouting.org/iproute2.doc.html iproute2 documentation].

+

The {{Pkg|moreutils}} package provides useful tools like {{man|1|sponge}} that are missing from the GNU coreutils.

−

−

The [[Network configuration]] article shows how the ''ip'' command is used in practice for various common tasks.

−

−

{{Note|You might be familiar with the [[Wikipedia:ifconfig|ifconfig]] command, which was used in older versions of Linux for interface configuration. It is now deprecated in Arch Linux; you should use ''ip'' instead. }}

−

−

== locate ==

−

−

[[Install]] the {{Pkg|mlocate}} package. The package contains an {{ic|updatedb.timer}} unit, which invokes a database update each day. The timer is enabled right after installation, [[start]] it manually if you want to use it before reboot. You can also manually run ''updatedb'' as root at any time. By default, paths such as {{ic|/media}} and {{ic|/mnt}} are ignored, so ''locate'' may not discover files on external devices. See {{man|8|updatedb}} for details.

−

−

The ''locate'' command is a common Unix tool for quickly finding files by name. It offers speed improvements over the [[wikipedia:Find|find]] tool by searching a pre-constructed database file, rather than the filesystem directly. The downside of this approach is that changes made since the construction of the database file cannot be detected by ''locate''. This problem is minimised by regular, typically scheduled use of the ''updatedb'' command, which (as the name suggests) updates the database.

−

−

Before ''locate'' can be used, the database will need to be created. To do this, execute {{ic|updatedb}} as root.

−

−

See also [http://jvns.ca/blog/2015/03/05/how-the-locate-command-works-and-lets-rewrite-it-in-one-minute/ How locate works and rewrite it in one minute].

−

−

== less ==

−

−

{{Expansion|less is a complex beast, and this section should explain some of the basic less commands}}

−

−

[[Wikipedia:less (Unix)|less]] is a terminal pager program used to view the contents of a text file one screen at a time. Whilst similar to other pagers such as [[Wikipedia:more (command)|more]] and [[Wikipedia:pg (Unix)|pg]], ''less'' offers a more advanced interface and complete [http://www.greenwoodsoftware.com/less/faq.html feature-set].

−

−

See [[List of applications#Terminal pagers]] for alternatives.

−

−

=== Vim as alternative pager ===

−

−

[[Vim]] includes a script to view the content of text files, compressed files, binaries, directories. Add the following line to your shell configuration file to use it as a pager:

−

{{hc|~/.bashrc|2=alias less='/usr/share/vim/vim80/macros/less.sh'}}

−

There is also an alternative to ''less.sh'' macro, which may work as the {{ic|PAGER}} environment variable. Install {{Pkg|vimpager}} and add the following to your shell configuration file:

+

== Alternatives ==

−

{{hc|~/.bashrc|2=

−

export PAGER='vimpager'

−

alias less=$PAGER

−

}}

−

Now programs that use the {{ic|PAGER}} environment variable, like [[git]], will use ''vim'' as pager.

+

Alternatives to the core utilities in the {{Grp|base}} group are [[BusyBox]], the [[Heirloom|Heirloom Toolchest]], {{Pkg|9base}}, {{AUR|sbase-git}} and {{AUR|ubase-git}}.

−

== ls ==

+

=== cp alternatives ===

−

[[Wikipedia:ls|ls]] lists directory contents.

+

Using [[rsync#As cp/mv alternative]] allows you to resume a failed transfer, to show the transfer status, to skip already existing files and to make sure of the destination files integrity using checksums.

−

See {{ic|info ls}} or [http://www.gnu.org/software/coreutils/manual/html_node/ls-invocation.html#ls-invocation the online manual] for more information.

For graphical file searchers, see [[List of applications/Utilities#File searching]].

−

{{hc|$ ls -l ''/path/to/directory''|

+

=== diff alternatives ===

−

total 128

−

drwxr-xr-x 2 archie users 4096 Jul 5 21:03 Desktop

−

drwxr-xr-x 6 archie users 4096 Jul 5 17:37 Documents

−

drwxr-xr-x 2 archie users 4096 Jul 5 13:45 Downloads

−

-rw-rw-r-- 1 archie users 5120 Jun 27 08:28 customers.ods

−

-rw-r--r-- 1 archie users 3339 Jun 27 08:28 todo

−

-rwxr-xr-x 1 archie users 2048 Jul 6 12:56 myscript.sh

−

}}

−

The {{ic|total}} value represents the total disk allocation for the files in the directory, by default in number of blocks.

+

While {{Pkg|diffutils}} does not provide a word-wise diff, several other programs do:

−

−

Below, each file and subdirectory is represented by a line divided into 7 metadata fields, in the following order:

−

−

* type and permissions:

−

** the first character is the entry type, see {{ic|info ls -n "What information is listed"}} for an explanation of all the possible types; for example:

−

*** {{ic|-}} denotes a normal file;

−

*** {{ic|d}} denotes a directory, i.e. a folder containing other files or folders;

−

*** {{ic|p}} denotes a named pipe (aka FIFO);

−

*** {{ic|l}} denotes a symbolic link;

−

** the remaining characters are the entry's [[permissions]];

−

* number of [[Wikipedia:Hard link|hard links]] for the entity; files will have at least 1, i.e. the showed reference itself; folders will have at least 2: the showed reference, the self-referencing {{ic|.}} entry, and then a {{ic|..}} entry in each of its subfolders;

−

* owner [[user]] name;

−

* [[group]] name;

−

* size;

−

* last modification timestamp;

−

* entity name.

−

−

=== File names containing spaces enclosed in quotes ===

−

−

By default, file and directory names that contain spaces are displayed surrounded by single quotes. To change this behavior use the {{ic|-N}} or {{ic|1=--quoting-style=literal}} options. Alternatively, set the {{ic|QUOTING_STYLE}} [[environment variable]] to {{ic|literal}}. [https://unix.stackexchange.com/questions/258679/why-is-ls-suddenly-surrounding-items-with-spaces-in-single-quotes]

−

−

== lsblk ==

−

−

{{man|8|lsblk}} will show all available [[w:Device_file#Block_devices|block devices]] along with their partitioning schemes, for example:

−

−

{{hc|$ lsblk -f|

−

NAME FSTYPE LABEL UUID MOUNTPOINT

−

sda

−

├─sda1 vfat C4DA-2C4D /boot

−

├─sda2 swap 5b1564b2-2e2c-452c-bcfa-d1f572ae99f2 [SWAP]

−

└─sda3 ext4 56adc99b-a61e-46af-aab7-a6d07e504652 /

−

}}

−

−

The beginning of the device name specifies the type of block device. Most modern storage devices (e.g. hard disks, [[SSD]]s and USB flash drives) are recognised as SCSI disks ({{ic|sd}}). The type is followed by a lower-case letter starting from {{ic|a}} for the first device ({{ic|sda}}), {{ic|b}} for the second device ({{ic|sdb}}), and so on. ''Existing'' partitions on each device will be listed with a number starting from {{ic|1}} for the first partition ({{ic|sda1}}), {{ic|2}} for the second ({{ic|sda2}}), and so on. In the example above, only one device is available ({{ic|sda}}), and that device has three partitions ({{ic|sda1}} to {{ic|sda3}}), each with a different [[file system]].

−

−

Other common block device types include for example {{ic|mmcblk}} for memory cards and {{ic|nvme}} for [[NVMe]] devices. Unknown types can be searched in the [https://www.kernel.org/doc/Documentation/devices.txt kernel documentation].

−

−

== mkdir ==

−

−

[[Wikipedia:mkdir|mkdir]] makes directories.

−

−

To create a directory and its whole hierarchy, the {{ic|-p}} switch is used, otherwise an error is printed. As users are supposed to know what they want, {{ic|-p}} switch may be used as a default:

−

−

alias mkdir='mkdir -p -v'

−

−

The {{ic|-v}} switch make it verbose.

−

−

Changing mode of a just created directory using ''chmod'' is not necessary as the {{ic|-m}} option lets you define the access permissions.

−

−

{{Tip|If you just want a temporary directory, a better alternative may be [[Wikipedia:Temporary file|mktemp]]: {{ic|mktemp -p}}.}}

−

−

== mv ==

−

−

[[Wikipedia:mv|mv]] moves and renames files and directories.

−

−

To limit potential damage caused by the command, use an alias:

−

−

alias mv='timeout 8 mv -iv'

−

−

This alias suspends ''mv'' after eight seconds, asks for confirmation before overwriting any existing files, lists the operations in progress and does not store itself in the shell history file if the shell is configured to ignore space starting commands.

−

−

== od ==

−

−

The [[Wikipedia:od (Unix)|od]] (''o''ctal ''d''ump) command is useful for visualizing data that is not in a human-readable format, like the executable code of a program, or the contents of an unformatted device. See the [http://www.gnu.org/software/coreutils/manual/html_node/od-invocation.html#od-invocation manual] for more information.

−

−

== pv ==

−

−

You can use {{Pkg|pv}} (''pipe viewer'') to monitor the progress of data through a pipeline, for example:

In most cases {{ic|pv}} functions as a drop-in replacement for {{ic|cat}}.

−

−

== rm ==

−

−

[[Wikipedia:rm_(Unix)|rm]] removes files or directories.

−

−

To limit potential damage caused by the command, use an alias:

−

−

alias rm='timeout 3 rm -Iv --one-file-system'

−

−

This alias suspends ''rm'' after three seconds, asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems and does not store itself in the shell history file if the shell is configured to ignore space starting commands. Substitute {{ic|-I}} with {{ic|-i}} if you prefer to confirm even for one file.

−

−

Zsh users may want to put {{ic|noglob}} before {{ic|timeout}} to avoid implicit expansions.

−

−

To remove directories known to be empty, use ''rmdir'' as it fails in case of files inside the target.

−

−

== sed ==

−

−

[[Wikipedia:sed|sed]] is stream editor for filtering and transforming text.

−

−

Here is a handy [http://sed.sourceforge.net/sed1line.txt list] of ''sed'' one-liners examples.

−

−

{{Tip|More powerful alternatives are [[Wikipedia:AWK|AWK]] and even [[Wikipedia:Perl|Perl]] language.}}

−

−

== seq ==

−

−

''seq'' prints a sequence of numbers. Shell built-in alternatives are available, so it is good practice to use them as explained on [[Wikipedia:Seq (Unix)|Wikipedia]].

−

−

== ss ==

−

−

''ss'' is a utility to investigate network ports and is part of the {{Pkg|iproute2}} package in the {{Grp|base}} group. It has a similar functionality to the [https://www.archlinux.org/news/deprecation-of-net-tools/ deprecated] netstat utility.

−

−

Common usage includes:

−

−

Display all TCP Sockets with service names:

−

$ ss -at

−

−

Display all TCP Sockets with port numbers:

−

$ ss -atn

−

−

Display all UDP Sockets:

−

$ ss -au

−

−

For more information see {{man|8|ss}} or {{ic|ss.html}} from the {{pkg|iproute2-doc}} package.

−

−

== tar ==

−

−

As an early Unix archiving format, .tar files—known as "tarballs"—are widely used for packaging in Unix-like operating systems. Both [[pacman]] and [[AUR]] packages are compressed tarballs, and Arch uses [[GNU Project|GNU's]] ''tar'' program by default.

−

−

For .tar archives, ''tar'' by default will extract the file according to its extension:

''wipefs'' can list or erase [[file system]], [[RAID]] or [[partition|partition-table]] signatures (magic strings) from the specified device. It does not erase the file systems themselves nor any other data from the device.

+

The following three tools aim to replace grep for code search. They do recursive search by default, skip binary files and respect {{ic|.gitignore}}.

Latest revision as of 03:37, 31 July 2019

Core utilities are the basic, fundamental tools of a GNU/Linux system. On Arch Linux they are found in the base group. This article provides an incomplete overview of them, links their documentation and describes useful alternatives. The scope of this article includes, but is not limited to, the GNU coreutils. Most core utilities are traditional Unix tools (see Heirloom) and many were standardized by POSIX but have been developed further to provide more features.

Most command-line interfaces are documented in man pages, utilities by the GNU Project are documented primarily in Info manuals, some shells provide a help command for shell builtin commands. Additionally most utilities print their usage when run with the --help flag.

Preventing data loss

rm, mv, cp and shell redirections happily delete or overwrite files without asking. rm, mv, and cp all support the -i flag to prompt the user before every removal / overwrite. Some users like to enable the -i flag by default using aliases. Relying upon these shell options can be dangerous, because you get used to them, resulting in potential data loss when you use another system or user that does not have them. The best way to prevent data loss is to create backups.

Alternatives

cp alternatives

Using rsync#As cp/mv alternative allows you to resume a failed transfer, to show the transfer status, to skip already existing files and to make sure of the destination files integrity using checksums.